Density estimation for amorphous carbon nanopillars grown by focused ion beam assisted chemical vapor deposition

The mechanical resonant frequency and spring constant of amorphous carbon nanopillars grown by focused ion beam assisted chemical vapor deposition (FIB CVD) were measured to evaluate the pillar density. The measured density ranged from 2.5 to 4.2×3 kg/m3, depending on the growth conditions. Annealing the pillars at 600 °C completely removed the Ga incorporated in the pillar during FIB CVD. The pillar density after annealing decreased to about 1.9×103 kg/m3, which indicated the density excess was mainly due to the implantation of Ga. At lower growth rates, a sharp decrease in the Ga content suggested higher sputtering rate of Ga through ion beam irradiation.